EP1503388B1 - Magnetic metal particle aggregate - Google Patents

Magnetic metal particle aggregate Download PDF

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Publication number
EP1503388B1
EP1503388B1 EP04018027.5A EP04018027A EP1503388B1 EP 1503388 B1 EP1503388 B1 EP 1503388B1 EP 04018027 A EP04018027 A EP 04018027A EP 1503388 B1 EP1503388 B1 EP 1503388B1
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particles
magnetic metal
phase
particle
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German (de)
English (en)
French (fr)
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EP1503388A3 (en
EP1503388A2 (en
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Kimitaka DOWA MINING CO. LTD. Sata
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Dowa Electronics Materials Co Ltd
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Dowa Electronics Materials Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
    • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
    • B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • B22F1/0545—Dispersions or suspensions of nanosized particles
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/047—Making non-ferrous alloys by powder metallurgy comprising intermetallic compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/0036—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties showing low dimensional magnetism, i.e. spin rearrangements due to a restriction of dimensions, e.g. showing giant magnetoresistivity
    • H01F1/0045—Zero dimensional, e.g. nanoparticles, soft nanoparticles for medical/biological use
    • H01F1/0054—Coated nanoparticles, e.g. nanoparticles coated with organic surfactant
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/06—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder
    • H01F1/065—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder obtained by a reduction
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
    • H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
    • H01F1/06—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder
    • H01F1/068—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder having a L10 crystallographic structure, e.g. [Co,Fe][Pt,Pd] (nano)particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y25/00—Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F10/00—Thin magnetic films, e.g. of one-domain structure
    • H01F10/007—Thin magnetic films, e.g. of one-domain structure ultrathin or granular films
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12014—All metal or with adjacent metals having metal particles
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12181—Composite powder [e.g., coated, etc.]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12993—Surface feature [e.g., rough, mirror]

Definitions

  • This invention relates to a magnetic metal particle aggregate whose particles contain Fe and Pt as alloying elements which can be used in high-density magnetic recording media, nanoscale electronic devices, permanent magnet materials, biomolecular labeling agents, drug carriers and the like, and to a method of producing the magnetic metal particle aggregate.
  • reaction site is a water/oil type reversed micelle utilizing an octane oil phase and CTAB (cetyl trimethyl ammonium bromide) as a surfactant.
  • CTAB cetyl trimethyl ammonium bromide
  • the nanometer size FePt particles obtained by these methods has a disordered fcc (face-centered cubic) crystal structure, and exhibit superparamagnetism at room temperature. These particles could be made ferromagnetic by heat-treating the same and transforming the crystal structure to an L1 0 ordered fct (face-centered tetragonal) type.
  • the heat treatment has to be conducted at or above the crystal structure transition (disordered to ordered phase) temperature (T t ), which is 500 °C or higher.
  • T t crystal structure transition (disordered to ordered phase) temperature
  • the particle size distribution broadens owing to particle growth caused by heat-induced coalescence among the particles.
  • the particles consist of a mixture of single and multi-domain structures that makes them unsuitable for a high-density magnetic recording media. Therefore, in order to obtain FePt particles having ferromagnetism while maintaining their particle diameter immediately after synthesis, it is effective to coat the particles with a protective agent for preventing inter-particle coalescence or to lower T t by some method so that the heat treatment can be conducted at lower temperature.
  • the researchers synthesized FePt particles by heating a solution of Fe (acac) 3 and Pt (acac) 2 in tetraethylene glycol under stirring and refluxing at different temperatures up to the boiling point. They found that the products synthesized at reaction temperatures above 280 °C exhibited XRD peaks of 001 and 110 lattice planes corresponding to fct-FePt and concluded that the FePt particles including fct structure can be directly synthesized from liquid phase. However, the transmission electron micrographs of the FePt particles suggested that the particles were not in a dispersed state but were coalesced.
  • FePt nanoparticles of the type discussed in the foregoing are used in high-density magnetic recording media, nanoscale electronic devices, permanent magnet materials, biomolecular labeling agents, drug carriers and the like
  • a processing technique is necessary to assemble the FePt nanoparticles with specific magnetic characteristics on a substrate or base at prescribed inter-particle spacing in either one, two or three dimensions.
  • an additional process to coat the particles with some substance, a reagent for example becomes necessary.
  • Such operations are best conducted with FePt nanoparticles dispersions; where particles are separated from each other and retain a prescribed inter-particle distance.
  • References 1-4 cannot readily produce fct-FePt nanoparticle dispersion because the particles have to be subjected to heat treatment at 500 °C or higher in order to obtain the fct structure.
  • the synthesis method described in Reference 4 is very likely to be capable of directly synthesizing fct-FePt particles but, as can be seen from the transmission electron micrographs in the paper, the particles were strongly agglomerated and were not successfully dispersed. This is attributed to the particle production history.
  • WO 02/062509 A1 discloses a method for preparing fine particles comprising a transition metal and a noble metal which are monodisperse and have almost no particle diameter distribution, and are transferable to a CuAu-I type LI 0 ordered phase.
  • a salt or a complex of at least one transition metal selected from Fe and Co and a salt of a complex of at least one transition metal selected from Pt and Pd is dissolved in an organic solvent miscible with water or an alcohol in the presence of an organic protecting agent, and the resultant solution is heated under reflux in the presence of an alcohol in an inert atmosphere, to thereby prepare a binary alloy comprising a transition metal and a noble metal, or, a salt or a complex of at least one element selected from the group of Cu, Bi, Sb, Sn, Pb and Ag is further dissolved in the above solvent and the resultant solution is heated under reflux in the presence of an alcohol in an inert atmosphere, to thereby prepare a ternary alloy comprising a transition metal, a noble metal and
  • U.S. 5,094,767 A discloses highly viscous magnetic fluids, essentially consisting of superparamagnetic solid particles coated with a surfactant and colloidally dispersed in a carrier liquid.
  • An object of the present invention is therefore to provide such an aggregate.
  • the inventor succeeded in obtaining an aggregate of nanoparticles including fct structure whose particles are dispersed with a prescribed inter-particle distance.
  • the present invention provides a magnetic metal particle aggregate composed of magnetic metal particles whose main components and the contents thereof are represented by the following general formula (1): [T X M 1-X ] Y Z 1-Y (1), where T is one or both of Fe and Co, M is one or both of Pt and Pd, Z is at least one member selected from the group composed of Ag, Cu, Bi, Sb, Pb and Sn, X represents 0.3 ⁇ 0.7, and Y represents 0.7 ⁇ 1.0, the balance being impurities unavoidably incorporated during production, wherein the proportion of the fct structure is in the range of 10 ⁇ 100%, the particles which were estimated to have an average diameter of 30 nm or less preferably of 10 nm or less from transmission electron microscopic observation (TEM), are in the dispersed state, spaced apart from one another, preferably by an inter-particle distance of 1 nm or greater.
  • T is one or both of Fe and Co
  • M is one or both of Pt and Pd
  • Z is at least one
  • the magnetic metal particle aggregate in accordance with the present invention can exist in a state having overall fluidity or can exist in a state with the individual particles located at prescribed positions (fixed).
  • the magnetic metal particle aggregate (assembly) of this invention can be obtained by a method comprising the following step:
  • This method is enable to make the magnetic metal particle aggregates in which the particles are in a dispersed state spaced apart from one another.
  • the aforesaid liquid organic medium (A) may be an alcoholic liquid and the liquid organic medium (B) may be an organic liquid whose water solubility is less than 1 wt.% and boiling point is less than 200 °C, preferably less than 100 °C.
  • the liquid organic medium (A) can be a post-reaction liquid obtained when FePt nanoparticles having fct structure as a part or all are directly synthesized by the polyol process.
  • the aforesaid dispersion can be achieved by coating the particle with a surface-active agent.
  • the magnetic metal particles are preferably dispersed in a liquid medium at an inter-particle distance of 1 nm or greater, the concentration of the magnetic metal particles in the dispersion is preferably not less than 1.0 x 10 -5 vol. % and not greater than 40 vol. %.
  • the average particle diameter of the magnetic metal particles by the dynamic light scattering method is 30 nm or less, preferably 10 nm or less.
  • the dispersion medium at this time is preferably constituted from the organic liquid (B) whose water solubility is less than 1 wt.
  • % and boiling point is less than 200°C
  • a surface active agent composed of an organic medium (C) whose molecule includes at least one radical selected from the group consisting of an amine, amide, azo, carboxyl, sulfone, sulfine, phosphone, phosphine, carboxylate, phosphonate, phosphinate, sulfonate, sulfinate or thiol radical.
  • the particles can be distributed on the surface of a substrate in a single layer or multiple layers in a state spaced from one another by 1 nm or greater.
  • Figure 1 is an example of magnetic metal particle aggregate according to the present invention.
  • Figure 1 is the transmission electron micrograph (X300,000) of FePt particle aggregate obtained in Example 1 set out later in this specification.
  • the aggregate is composed of particles of substantially equal diameter that are uniformly dispersed with constant inter-particle spacing.
  • This micrograph was taken with JEM-100CX II Transmission Electron Microscope (product of JEOL) at an acceleration voltage of 100 kV.
  • the observed sample was prepared by dripping the dispersion containing FePt particles onto a carbon coated Cu 150 mesh. The excess liquid was removed by using a filter paper (dripping and removal of excess liquid were repeated) and the mesh was dried naturally.
  • the proportion of face-centered tetragonal structure (proportion accounted for by L1 0 orderly phase constituting the fct structure) of the FePt particle aggregate was 52%.
  • the particles had an average particle diameter of 5.2 nm, a standard deviation of 1.0 nm, a geometrical average particle diameter of 5.1 nm and a geometrical standard deviation of 1.2 nm.
  • FePt nanoparticles including fct structure without heat treatment is suggested by Reference 4, for example.
  • the FePt nanoparticles including fct structure reported in Reference 4 are not monodispersed.
  • the FePt nanoparticles including fct structure according to the present invention are obtained in the form of an aggregate whose particles are uniformly dispersed at substantially even intervals.
  • the average inter-particle distance between particles is 3.3 nm as determined in accordance with Equation (B) set out in detail later.
  • the particles are configured to spread out two-dimensionally with this inter-particle spacing so as to form a single layer on a substrate (specimen stage).
  • the reason why the particles assume constant spacing in this manner can be considered to be because of the presence of a steric hindrance between the particles (in the illustrated case, adherence between particles is hindered by an inter-particle repulsive action owing to the presence of surface active agent).
  • the particles When the particles are immobilized on a substrate in a dispersed condition as shown in Figure 1 , they can, in that form, constitute a high-density magnetic recording medium, nanoscale electronic device, permanent magnet material, biomolecular labeling agent or drug carrier. Immobilization of the particles can be achieved by using a resinous, vitreous, ceramic or other insulating material and make them adhere at their respective locations. Coating and vapor depositing can be mentioned as ways of using the adhesive material to fix the particles. The adhesion can also be done using a coupling agent capable of chemically bonding inorganic and organic materials, such as a silane-coupling agent. In such a case, the particles can be uniformly distributed on the substrate to form a monolayer, as shown in Figure 1 , or, if required, multiple layers.
  • a coupling agent which can be represented by a general formula R'M(OR) 3 , where R' represents the organofunctional radical such as vinyl radical, epoxy radical, styryl radical, methacryl radical, amino radical, mercapto radical, chloropropyl radical, and the likes, OR represents a hydrolytic alkoxy radical or alkyl radical bound to M (Si, Ti, Zr, Al etc.).
  • R' represents the organofunctional radical such as vinyl radical, epoxy radical, styryl radical, methacryl radical, amino radical, mercapto radical, chloropropyl radical, and the likes
  • OR represents a hydrolytic alkoxy radical or alkyl radical bound to M (Si, Ti, Zr, Al etc.).
  • the alkoxide radical in the structure of these coupling agents reacts with the OH radical on an inorganic material surface, while the organofunctional radical chemically reacts with various organic materials.
  • the organofunctional radical includes, but not limited to a radical that can form a coordinate bond with a metal, namely an amine, amide, azo, carboxyl, sulfone, sulfine, phosphone, phosphine, carboxylate, phosphonate, phosphinate, sulfonate, sulfinate or thiol radical
  • the organofunctional radical can form a coordinate bond with an inorganic surface.
  • the properties of the coupling agent can also be used to attach nanoparticles on the surfaces of specific particles with diameter larger than the FePt nanoparticles, thereby enabling to be used as biomolecular labeling agents and drug carriers.
  • magnetic nanoparticles to uniform spherical particles of large particle diameter (e.g., organic particles of polystyrene or inorganic particles of SiO 2 ), it is possible to create nanoscale electronic devices with new capabilities that have not been achieved up to now.
  • nanoscale order magnetic metal particles pose durability problems, this can be overcome by coating the magnetic nanoparticles with a layer of M oxide (M being that in the foregoing equation).
  • Another attachment method that can be used to selectively configure the magnetic nanoparticles on a substrate or base is to form an insulating material pattern on a substrate or base made of an electrically conductive material and then apply a voltage to the conductive material.
  • the magnetic metal particle aggregate of the present invention satisfies these requirements apparently.
  • T X ⁇ M 1 - X Y ⁇ Z 1 - Y
  • T is one or both of Fe and Co
  • M is one or both of Pt and Pd
  • Z is at least one member selected from the group composed of Ag, Cu, Bi, Sb, Pb and Sn.
  • T and M are typically Fe and Pt.
  • X 0.5 is ideal for forming a face-centered tetragonal structure, a 10 ⁇ 100% face-centered tetragonal structure can be obtained in the range of X of 0.3 ⁇ 0.7.
  • the Z component can lower the crystal structure transition temperature (Tt) from fcc to fct structure in the case of synthesizing FePt particles by the polyol method, it need not be contained in some cases.
  • the optimum value of Y although differing depending on the type of Z, falls in the range of 0.7 ⁇ 1.0. A value of less than 0.7 for Y is undesirable because the resulting presence of excessive Z sharply depresses magnetic characteristics by hindering the emergence of fct structure.
  • Analysis of the composition of the magnetic metal particles according to the present invention can be carried out by EDX (energy dispersive X-ray) measurement.
  • the magnetic metal powder is ideally made up of metal particles having the composition represented by Equation (1), presence of impurities unavoidably incorporated in the course of production can be tolerated.
  • the composition of the magnetic metal particles according to the present invention is typically FePt, the ensuing explanation will be made using FePt particles as an example.
  • FePt particles is, by definition, to be construed as referring to magnetic metal particles represented by Equation (1).
  • the ratio of the face-centered tetragonal (fct) structure of the invention magnetic metal particles is therefore defined as 10 ⁇ 100 %, preferably 20 ⁇ 100 %, ,more preferably 55 ⁇ 100 %.
  • the crystal structure of the FePt particles can be ascertained by analyzing the volumetric ratio of the ferromagnetic structure determined by Mossbauer spectroscopy measurement of Fe atoms.
  • the breakdown of different crystal structures is generally determined by comparing X-ray diffraction peak intensities.
  • it is difficult to quantify the crystal structures of the invented FePt particles from these peaks because the X-ray diffraction patterns of the fcc structure and the fct structure are nearly identical and the intensities of the (001) and (110) reflections obtained only from the fct structure are very weak.
  • the volumetric fraction of the fct structure of the FePt particles is determined by calculating the fraction of magnetically ordered Fe atoms determined by Mössbauer spectroscopy measurement, and the so-obtained ratio is defined as the volumetric fraction of the fct structure.
  • the magnetic metal particle aggregate according to the present invention has an average particle diameter by transmission electron microscopic observation (TEM) of 30 nm or less, preferably 10 nm or less.
  • the aggregate is in a monodispersed state with the individual particles spaced apart, preferable at an inter-particle interval of 1 nm or greater.
  • the particle diameter, particle size distribution and inter-particle interval of the particles can be evaluated by TEM observation, and the particle size distribution thereof in a liquid can be evaluated by the dynamic light scattering method. Since measurement by the dynamic light scattering method is not possible when the particle concentration is low, it is necessary in such a case to first carry out an operation for increasing the concentration such as by evaporating the solvent.
  • the FPAR1000 Fiber-Optics Particle Analyzer manufactured by Otsuka Electronics Co., Ltd. is one of a number of dynamic light scattering-type particle distribution measuring units available.
  • the inter-particle interval is defined as follows in the case where the particles are dispersed in a single layer with two-dimensional spread.
  • a region including 500 or more particles is selected from a transmission electron micrograph of the particles.
  • the area of the region is calculated and defined as S and the number of particles therein is counted and defined as N.
  • the average particle diameter of the region is designated as r.
  • the inter-particle interval depends on the steric repulsion (steric hinderance) between the particles.
  • the inter-particle interval can be adjusted between 1 nm and 100 nm depending on the type of surface-active agent.
  • the inter-particle interval can be increased starting from the smallest value of the aforesaid inter-particle interval as the lower limit by reducing the particle concentration.
  • the magnetic metal particle agregate according to the present invention has an onset temperature (crystal structure transition starting temperature from fcc to fct ) of 400 °C or lower, saturation magnetization ⁇ s of 5 Am 2 /kg - 96.16 Am 2 /kg and coercivity Hc of 79 kA/m -3820 kA/m.
  • the magnetic characteristics (Hc, ⁇ s) can be measured with a SQUID magnetometer or a vibrating sample magnetometer (VSM), depending on the type of specimen.
  • Immiscible liquid organic mediums (A) and (B) and an appropriate surface-active agent (C) are prepared.
  • the liquid organic medium (A) is an alcoholic liquid
  • the liquid organic medium (B) is a liquid whose water solubility is less than 1 wt.% and boiling point is lower than 200 °C, preferably lower than 100 °C.
  • An organic medium (C) serving as a surface-active agent (dispersant) is also prepared.
  • a specific example of the organic medium (A) is a post-reaction liquid obtained when FePt nanoparticles including fct structure are directly synthesized by polyol process.
  • the organic medium A and a mass of FePt nanoparticles (P) are combined to prepare a liquid (A + P), and the organic medium (C) constituting the surface active agent is added to the organic medium (B) to prepare a liquid (B + C).
  • the liquid (A + P) and the liquid (B + C) are mixed and forcibly stirred (or shaken) to form particles (CP) composed of the particles (P) surface-coated with the organic medium (C).
  • phase A which consists mainly of organic medium (A) and has a relatively small amount of suspended particles (CP)
  • phase B phase which consists mainly of organic medium (B) and has a relatively large amount of suspended particles (CP).
  • the phase A is removed to recover the phase B.
  • the recovered phase B contains the particles P in a state coated to a certain thickness with the surface active agent C.
  • the particles experience an inter-particle repulsive action owing to the effect of the affinity towards the medium and an electrostatic repulsive force and are therefore dispersed in the liquid B by the inter-particle repulsive action.
  • an coherent mass of FePt nanoparticles (P) and the organic medium (C) constituting the surface active agent are added to the organic medium A to prepare a liquid (A + P + C).
  • the organic medium (C) constituting the surface active agent is also added to the organic medium B to prepare a liquid (B + C).
  • the liquid (A + P + C) and the liquid (B + C) are mixed and forcibly stirred (or shaken) to form particles (CP) composed of the particles (P) surface-coated with the organic medium (C).
  • phase A which consists mainly of organic medium (A) and has a relatively small amount of suspended particles (CP)
  • phase B phase which consists mainly of organic medium (B) and has a relatively large amount of suspended particles (CP).
  • the phase A is removed to recover the phase B.
  • the recovered phase B contains the particles P in a state coated to a certain thickness with the surface active agent C.
  • the particles experience an inter-particle repulsive action owing to the effect of the affinity towards the medium and an electrostatic repulsive force and are therefore dispersed in the liquid B by the inter-particle repulsive action.
  • a coherent mass of FePt nanoparticles (P) and the organic medium (C) constituting the surface active agent are added to the organic medium A to prepare a liquid (A + P + C).
  • the organic medium B is prepared.
  • the liquid (A + P + C) and the liquid (B) are mixed and forcibly stirred (or shaken) to form particles (CP) composed of the particles (P) surface-coated with the organic medium (C).
  • phase A which consists mainly of organic medium (A) and has a relatively small amount of suspended particles (CP)
  • phase B phase which consists mainly of organic medium (B) and has a relatively large amount of suspended particles (CP).
  • the phase A is removed to recover the phase B.
  • the recovered phase B contains the particles P in a state coated to a certain thickness with the surface active agent C.
  • the particles experience an inter-particle repulsive action owing to the effect of the affinity towards medium and an electrostatic repulsive force and are therefore dispersed in the liquid B by the inter-particle repulsive action.
  • first, second and third methods are production methods common in the points of:
  • the following refining method is preferably used to reduce the impurity content of the phase B obtained by the production method.
  • phase B obtained by the foregoing production method Water and/or alcohol is added to the phase B obtained by the foregoing production method, the obtained composite is forcibly stirred or shaken, and the resulting mixture is left to stand and/or centrifuged to phase-separate it into a phase (W) composed mainly of water/and or alcohol and having a relatively small amount of the particle (CP) suspension and a phase (B') composed mainly of organic medium (B) and having a relatively large amount of the particle (CP) suspension.
  • a phase B' is recovered from the so-separated phases and the obtained phase B' is dried as required by removing a desired amount of organic medium (B) therefrom.
  • a phase B' of low impurity concentration can be obtained by extracting the phase W to outside the system.
  • the organic medium A and organic medium B used in the present invention phase-separate.
  • the organic medium A can be a post-reaction liquid obtained when FePt nanoparticles including fct structure are directly synthesized by a polyol process. In this case, a mass of FePt nanoparticles are present in the post-reaction liquid.
  • the post-reaction liquid generally contains various constituents. The inventor measured the loss on heating of such a post-reaction liquid using a thermogravimetric and differential thermal analyzer (TG-DTA) and found that about 20% remained even when the temperature was increased to 400 °C. A solution containing components with such a high boiling point is not easy to deal with.
  • TG-DTA thermogravimetric and differential thermal analyzer
  • this type of post-reaction liquid can be advantageously used in the production method of this invention, because the amount of such high-boiling-point impurities, metal ions and the like transferred to the phase B side is small.
  • another organic medium B should have less than 1 wt.% water solubility and boiling point of lower than 200 °C.
  • the usable functional organic medium B includes, but not limited to hexane, cyclohexane, benzene, toluene, xylene, chloroform.
  • the organic medium B is easy to dry by heating and/or pressure reduction.
  • the impurities present in the medium B should be washed with water.
  • phase B it is also possible to use an alcohol (which will phase-separate from the organic medium B) either with water or alone. Even if the alcohol dissolves in the phase B, it can be easily removed by fractional distillation.
  • the organic medium C in the present invention is a surface active agent.
  • Preferable surface active agents for use in the present invention include ones consisting of an organic compound whose molecule includes an amine radical, amide radical or azo radical having an N atom that readily adheres to the metal particle surface, polyvinyl pyrrolidone, and organic compounds with sulfone, sulfine, phosphone, phosphine, carboxylate, phosphonate, phosphinate, sulfonate, sulfinate, thiol or carboxyl radical.
  • the mass concentration of impurities present in the phase B can be ascertained by calculating the total mass concentration of the organic medium (B), particles (CP) and organic medium (C) contained in the phase and then calculating the balance not accounted for.
  • the mass concentration of the organic medium (B), which has a boiling point of lower than 200 °C, can be found from the decrease in mass by drying, that of the particles (CP) can be found by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and that of the organic medium C can be ascertained by the analytical curve method using liquid chromatography or gas chromatography.
  • An impurity mass concentration exceeding 1 wt% is undesirable because it makes control of the dispersion liquid physical properties difficult and also becomes of cause of product and/or production equipment fouling.
  • Iron (III) acetylacetonate and platinum (II) acetylacetonate were added to 100 ml of tetraethylene glycol in an amount of 0.13 mmole each.
  • the liquid was stirred at 160 rpm with concurrent blow-in of nitrogen gas at a flow rate of 400 ml/min and reaction was continued with refluxing at 320 °C for 3.5 hr, whereby there was obtained a suspension containing precipitated fine particles of FePt.
  • the FePt particles were stuck together.
  • the suspension consisted of an organic medium (A) composed mainly of tetraethylene glycol (TEG) in which a mass of FePt nanoparticles (P) was present with the particles joined together (in a coherent state). This suspension will be designated (A + P).
  • the obtained suspension (A + P) was added with oleic acid and oleylamine as dispersant (surface active agent; organic medium C) in amounts to make the mole concentration of each four fold that of the total amount of metal in the suspension, whereafter the suspension was stirred for 1 hr at 80 °C and then shaken for 10 hr at a frequency of 5 Hz and stroke of 2 cm. By this there was obtained a suspension (A + P + C).
  • the mixture obtained was left to stand and then centrifuged to phase-separate it into a phase A composed mainly of the liquid A and a phase B composed mainly of the liquid B.
  • the phase A and phase B were fractionated. A large number of fine FePt particles were observed to be suspended in the liquid of the fractionated phase B.
  • phase B, 35 ml, and pure water, 35 ml were joined in a container and shaken for 10 hr at a frequency of 5 Hz and stroke of 2 cm.
  • the mixture obtained was left to stand and then centrifuged to phase-separate it into a phase W composed mainly of water and a phase B' composed mainly of liquid B.
  • the phase W and phase B' were fractionated. Fine FePt particles were observed to be suspended in the phase B'.
  • the obtained phase B' was observed with a transmission electron microscope (TEM).
  • the phase B' was prepared for the TEM observation by applying it to a substrate and then allowing it to dry naturally.
  • the average particle diameter was 5.2 nm
  • the standard deviation was 1.0 nm
  • the average inter-particle interval was 3.3 nm.
  • the geometrical average particle diameter was 5.1 and the geometrical standard deviation was 1.2.
  • the transmission electron micrograph of Figure 1 shows this state. As can be seen in Figure 1 , the particles are dispersed at substantially equal intervals to form a single-layer film extending two-dimensionally. From this it can be concluded that the particle surfaces are uniformly coated with the surface active agent to produce a steric repulsion (steric hindrance effect).
  • the particle concentration of the phase B' was 7.85 x 10 -4 wt% and the total concentration of the FePt nanoparticle aggregate, cyclohexane and surface active agent was 99.5%. The balance accounted for by impurities was therefore 0.5 wt% or less.
  • the average particle diameter measured by the dynamic light scattering method was 5 nm.
  • Example 1 was repeated except that the surface active agent (organic medium C) added to the cyclohexane side in Example 1 was instead all added to the (A + P + C) suspension side.
  • an (A + P + 2C) suspension was produced by the same method as in Example 1.
  • the (A + P + 2C) suspension, 35 ml, and the cyclohexane (organic medium B), 35 ml, were joined in a container and shaken for 10 hr at a frequency of 3 Hz and stroke of 10 cm, whereafter the process of Example 1 was repeated to obtain a phase B'.
  • the obtained phase B' was not substantially different from that of Example 1.
  • Example 1 Suspension (A + P + C) was obtained in the same manner as in Example 1, except the stirring for 1 hr at 80 °C was omitted. As in Example 1, the (B + C) liquid was added to the (A + P + C) suspension, whereafter the process of Example 1 was repeated to obtain a phase B'. The obtained phase B' was not substantially different from that of Example 1.
  • Example 1 Suspension (A + P + 2C) was obtained in the same manner as in Example 1, except that the surface-active agent (organic medium C) was added only to the (A + P + C) suspension side and the stirring for 1 hr at 80°C was omitted.
  • the (A+ P + 2C) suspension (35 ml) and the cyclohexane (organic medium B), (35 ml) were joined in a container and shaken for 10 hrs at a frequency of 3 Hz and stroke of 10 cm, thereafter the process of Example 1 was repeated to obtain a phase B'.
  • the phase B' thus was not substantially different from that of Example 1.
  • Example 1 Suspension (A + P) was prepared as in Example 1.
  • required amounts of oleic acid and oleylamine (organic medium C) were added to make the mole concentration of each four fold than that of the total amount of metal concentration in the suspension, thereafter the suspension was shaken for 5 hrs at a frequency of 3 Hz and stroke of 10 cm, exposed to an ultrasonic wave for 1 hr, and further shaken for 5 hrs at a frequency of 3 Hz and stroke of 10 cm, thereby preparing an (A + P + C) suspension.
  • the (A + P + C) suspension was mixed with (B + C), thereafter the process in Example 1 was repeated to obtain a phase B'.
  • the obtained phase B' was not substantially different from that of Example 1.
  • An ultrasonically treated (A + P + 2C) suspension was obtained in the same manner as in Example 5, except that the surface-active agent (organic medium C) was added only to the (A + P + C) suspension side.
  • the as-obtained (A + P + C) suspension (35 ml) and the cyclohexane (organic medium B) (35 ml) were joined in a container and shaken for 10 hrs at a frequency of 3 Hz and stroke of 10 cm, whereafter the process of Example 1 was repeated to obtain a phase B'.
  • the obtained phase B' was not substantially different from that of Example 1.
  • Iron (III) acetylacetonate and platinum (II) acetylacetonate were added to 100 ml of tetraethylene glycol in an amount of 0.13 mmole each.
  • the liquid was stirred at 160 rpm with concurrent blow-in of nitrogen gas at a flow rate of 400 ml/min and reaction was continued with refluxing at 320 °C for 3.5 hr, whereby there was obtained a suspension containing precipitated fine particles of FePt.
  • FIG. 1 is a transmission electron micrograph of the FePt particle aggregate obtained in this manner. As can be seen, the FePt particles were markedly cohered.
  • Iron (III) acetylacetonate and platinum (II) acetylacetonate were added to 100 ml of tetraethylene glycol in an amount of 0.13 mmole each.
  • the liquid was stirred at 160 rpm with concurrent blow-in of nitrogen gas at a flow rate of 400 ml/min and reaction was continued with refluxing at 320 °C for 3.5 hr, whereby there was obtained a suspension containing precipitated fine particles of FePt. The fine particles of FePt were stuck together..

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